Patent GB-744364-A (GB)
Title: Improvements in or relating to self-balancing electric bridge apparatus
Inventor: CLARK DAVID DUNCAN
IPC: G01R27/02
Filed: 1952-10-30
Abstract: 744,364. Electric indicating systems. GENERAL ELECTRIC CO., Ltd. Jan. 29, 1954 [Oct. 30, 1952; Jan. 23, 1953], Nos. 27343/52 and 2072/53. Class 40(1) In a self-balancing bridge circuit, the unbalance detector sets a counter into operation, forward or backwards, according to the sense of the unbalance, and the counter adjusts the balancing arm of the bridge by discrete steps to a value, corresponding to the counter setting, until balance is restored. The variable arm may be, e.g. a resistance-thermometer, a strain-gauge resistor or varied in accordance with pressure, water level or radio frequency power. The setting of the counter, which may be of binary or decade type and consist of relay chains., cold cathode discharge tube rings or uniselector switches, may be used to indicate the magnitude of the of the variable directly, or for transmitting it, e.g. by the pulse code telemetering system described in Specification 713,476. The unbalance detector is preferably a relay, switching of which to either of its two unbalance positions connects an electric pulse generator to the counter in the appropriate. sense. The bridge arms may be resistive, capacitative, or inductive. As described, for measuring temperature a platinum resistance thermometer, Fig. 1 is used as the variable arm of a bridge fed from an oscillator 8. The out-of-balance potential is amplified at 10 and passed through a phase sensitive rectifier' 12 to a relay 13 which in its two unbalance positions (Fig. 2, not shown) applies earth to terminals 80 or 81, Figs. 3, 4 according to the sense of the bridge unbalance, to set the reversible counter 6 which adjusts the resistor arm 5. Impulse generator, Fig. 3. Earthing of terminals 80 or 81 energizes forward or reverse counter relay pairs FA-FB, RA-RB, respectively. In either case a slow-acting relay A is energized which in turn energizes a relay B which de-energizes A. As A releases, it de-energizes B whereby A is re-energized. Relays A, B inter-act in this way to send equal markspace impulses to the counter, Fig. 3 over contact B2. Binary counter, Fig. 3. This comprises similar stages I, II ... X each consisting of two relays S-T, SA-TA, SB-TB, ... SI-TI. the relays S, SA, ... SI of which remove a short circuit from a corresponding resistor 61, 62 ... 70, Fig. 3 in the bridge balancing arm 5 as the associated counter stage goes from its "zero" to "one" condition. Assuming the counter to be set at zero, i.e., with all S, T, relays released, and the relays FA, FB set for forward operation, then the first impulse over contacts B2 energizes winding d of relay T which locks in series with relay S as the impulse ceases. The next impulse passes via operated contacts S1 to the winding of b to relay T to release it, and over contacts FA4 (operated) energizes the relay TA in stage II. At the end of the second impulse relay S in stage I releases and relay SA operates in series with TA in stage II. The third impulse operates relay T in stage I but does not affect stage II. At the end of the impulse relay S operates in series with T. At the fourth impulse relays T, TA release and relay TB in stage III (not shown) operates. As the fourth pulse ends relays S. SA release and SB in stage III operates. The values of the resistors 61, 62 ... 70 are in the ratio 1 : 2 : 4 : ... &c., so that as the counter stages are set as above described the resistance in the bridge arm 5 is increased in steps equal to the value of resistor 61 until balance is achieved when impulsing is stopped by release of relays FA. FB. Reverse setting of the counter is achieved in a similar manner by operation of the relays RA, RB causing the bridge arm 5 to be reduced in steps equal to the value of resistor 61. Indicating counter setting: One of the relays of each stage may be used to fire a cold cathode diode associated with the stage, the diodes of all the stages functioning as a local or remote indicator. Alternatively, the binary digital setting may be converted to analogue form to read temperature directly. Decade counter, Fig. 4. Each denominational stage of the counter comprises a ring of cold cathode tubes UVO, UVI, UV2 ... UV9 (units), TVO, TVI ... TV9 (tens) and HVO, HVI,.... (hundreds). The earth potential applied to contacts 80, 81 for forward and reverse operation, respectively, of the counter, operates relays A, S. Operation of either of these connects a relaxation oscillator 123 to the units counter stage. Each stage is such that when any one tube in the stage is fired, it positvely biases by way of a resistor 146 and contact such as SA1, SA2,... the trigger grid of the next succeeding tube in the stage, so that when.operating impulses are applied in parallel to the grids of all the tubes in any one stage the tubes fire in succession and a fired tube is extinguished as the next fires. The units stage is operated directly by the impulses from the oscillator. Transfer to the tens denominational stage is effected by pulsing the grids of all tubes therein over contact SB3 as the zero tube UVO is fired. Similarly the hundreds stage is pulsed over contacts SC6 as the tens "zero" tube TVO fires. When the relay S is operated for reverse counter operation, relays SA, SB, SC, SD are operated and switch the biasing potential resulting from the fired condition of any one tube to the preceding tube in a stage so that the tubes in each stage still fire in succession but in the reverse direction so that the count of incoming pulses is subtracted from the counter setting. As each tube fires it operates a corresponding relay UO, U1, ... U9 . (units), TO, T1, ... T9 (tens), HO, H1 ... H9 (hundreds) these relays switching resistance UR1, UR2 ... UR9, TR1...TR9, HR1...HR9 of value corresponding to the associated counter stage tube into the bridge arm 5 until balance is achieved. Additional contacts of the counter relays may be used for signalling the counter setting. The cold cathode tubes themselves may be used as a local indicator.